There are two general types of mechanical ventilation control modes. A first type delivers gas to a patient based on a frequency selected by the clinician which is independent of patient activity. This type of ventilation, known as controlled mechanical ventilation, is used when the ventilator is needed to breathe for the patient such as when the patient is non-alert, sedated, unresponsive or paralyzed. A second type of ventilation, known as assisted mechanical ventilation, or assisted ventilation, or augmented ventilation, delivers gas to the patient in response to an inspiratory effort generated by the patient. This type of ventilation helps the patient breathe, such as when the patient has respiratory insufficiency such as COPD. There are also ventilators and modes of ventilation that combine the two modes of ventilation described above.
In the use of all ventilators a gas delivery circuit is required to deliver the gas from the ventilator to the patient. Also required is a ventilation patient interface which is in communication with the patient's airway. The gas delivery circuit connects to the patient interface so that the ventilator can deliver air into the patient's airway through the gas delivery circuit and through the patient interface. These interfaces can be non-invasive such as a mask over the nose and/or mouth or a nasal cannula, or can be invasive, such as an endotracheal tube, tracheostomy tube, or transtracheal catheter which is placed into the airway of the patient.
In a more specific case of respiratory support ventilation, the patient receives gas from the ventilator with a patient interface configuration known as an “open airway” system, meaning the patient's respiratory tract is open to atmosphere through their normal upper airway breathing routes (mouth and nose). Open airway ventilation (OAV) when used is typically used with spontaneously breathing patients who need respiratory support; however, OAV can also be used for ventilator dependent patients who cannot breathe. In the former case, the patient may be breathing “spontaneously” or naturally through their upper airway but their breathing is augmented by receiving additional gas from the ventilator through the “open” patient interface. The goal of this therapy is to help the patient's work of breathing with an OAV system, such that the patient is not encumbered with the various problems, limitations, obtrusiveness and side effects of closed airway positive pressure ventilation. This system is described in U.S. Pat. No. 7,487,778 (Freitag) and US Printed Publication 2005/0005936 (Wondka). The ventilation interface described in this prior art is typically a transtracheal ventilation catheter that is placed percutaneously through the patient's neck into the tracheal lumen, or a catheter placed into an existing airway tube, such as an uncuffed tracheostomy tube. Alternatively, the ventilation catheter is placed into a stent or stoma guide, such as a Montgomery T-Tube, or an endotracheal tube, or an airway prosthesis. In OAV, providing mechanical ventilation support to the lungs is not obviously possible, because air delivered from the ventilator has the potential of leaking out of the upper airway if the airway is open, thus rendering the system ineffective and limiting the additive volume that can be delivered to the lung. Therefore, special airflow delivery fluid dynamics are required to make the system efficacious and efficient, and special delivery systems and interface designs are required to accomplish these dynamics.